In most current digital wireless systems, the traditional up-conversion chain (or significant portion thereof) is primarily analog and includes types such as super-heterodyne, low intermediate frequency (IF) and zero IF up-conversion technology. These technologies start with the conversion of inherently digital signals to analog signals through high performance digital-to-analog (D/A) converters, generally due to the higher frequencies involved. Once converted to the analog domain, various combinations of analog filters, amplifiers, mixers and modulators (and perhaps other analog elements) are cascaded to achieve the up-conversion from the output of the A/D converter(s) to the radio frequency (RF) band of interest (transmit RF signal).
Component variation, tolerances, and aging all affect the design requirements, costs, and manufacturability of the analog up-conversion (transmitter) and down-conversion (receiver) chains. One digital transmitter design, as described in U.S. Pat. No. 6,987,953 which is incorporated herein by reference, reduces or eliminates some or all of these problems by utilizing digital upconversion in the digital signal processing block. However, the output frequency is linked to the digital processing clock.
Accordingly, there is needed a digital transmitter that separates the digital signal processing from the RF translation. Utilization of digital frequency translation further allows for a transmitter design without the traditional need for high quality analog components.